Friday, March 24, 2017

Increased Blood Flow to the Brain Helped Human Intelligence

PhysOrg is running a story about research that focuses on the role that blood flow played in the evolution of human intelligence.  Roger Seymour writes:
My eureka moment occurred when I realised that the size of an artery can be gauged by the size of the hole in a bone that it passes through.

This meant that the rate of blood flow to the brain could be measured by the sizes of the carotid canals in fossil skulls from human evolution.

It was a nice idea, but it took the enthusiasm of my student Vanya Bosiocic to turn it into a piece of research. She travelled to museums in Australia and in South Africa, gaining access to priceless fossil hominin skulls to make the measurements.

We found that the size of the carotid canals increased much faster than expected from brain size in 12 species of our human ancestors over a period of 3 million years.

While brain size was increasing 3.5 times, blood flow rate surprisingly increased sixfold, from about 1.2ml per second to 7ml per second.

This indicates that our brains are six times as hungry for oxygen as those of our ancestors, presumably because our cognitive ability is greater and therefore more energy-intensive.
We require a huge amount of fuel to keep our brains functioning and, while correlation is never causation, there is a distinct correlation between our massive increase in brain size during the late Pliocene/early Pleistocene and the appearance of more sophisticated stone tools, evidence of hunting and, eventually control of fire.  One of the other factors that may have had a role in this was the increase in protein intake in the form of animal meat.  Human evolution is a very complex entity because as we evolved and our brains increased in size, we began to manipulate our surroundings in a more significant way.  This, in turn, changed how we adapted and evolved in response to them. 

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